1. Field of the Invention
The present invention relates to touch panels. More particularly the present invention relates to touch panels for display devices, wherein a substantially uniform gap between lower and upper substrates of the touch panel may be maintained.
2. Discussion of the Related Art
Touch panels have been developed as a means of efficiently interfacing with electronic devices via a display surface. For example, users may input desired information using a touch panel integrated with a display device while watching images displayed by the display device. Allowing users to input desired information to an electronic device via a display surface, touch panels substantially reduce or eliminate the need for other types of input devices (e.g., keyboards, mice, remote controllers, and the like). Currently, touch panels have been widely integrated with display surfaces of flat panel display devices such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescence (EL) devices, and cathode ray tubes (CRTs).
Depending on the type of contact object used (e.g., a user's finger, a stylus, etc.), and on the manner in which the location of a contact point (i.e., the location where the contact object is operably proximate the touch panel) is determined, touch panels are generally classifiable as analog resistive-type, capacitive-type, electromagnetic (EM)-type, saw-type, and infrared-type touch panels.
Generally, analog resistive-type touch panels include an upper substrate supporting upper electrodes and a lower substrate supporting lower electrodes. The upper and lower substrates are attached to each other but spaced apart from each other by a predetermined distance. When a surface of the upper substrate is contacted by a contact object, an upper electrode formed on the upper substrate electrically contacts a lower electrode formed on the lower substrate. When the upper and lower electrodes electrically contact each other, a voltage, made variable by a resistance value or a capacitance value specific to the location of where the user touched the touch panel (i.e., the contact point), is then detected and outputted along with a location defined by coordinates of the contact point.
Generally, capacitive-type touch panels include a film having a transparent electrode formed on a display device such as an LCD panel, wherein a voltage is applied to each corner of the film and a uniform electric field is thereby generated within the transparent electrode. Coordinates of the contact point may be determined in accordance with a voltage drop generated when the user touches the touch panel via a contact object.
FIG. 1 illustrates a plan view of a related art touch panel for a display device. FIG. 2 illustrates a cross-sectional view taken along line I–I′ of FIG. 1. FIG. 3 illustrates a cross-sectional view taken along line II–II′ of FIG. 1. FIG. 4 illustrates a cross-sectional view taken along line III–III′ of FIG. 1. FIG. 5A schematically illustrates an upper substrate of the related art touch panel shown in FIG. 1. FIG. 5B schematically illustrates a lower substrate of the related art touch panel shown in FIG. 1.
The related art touch panel shown in FIG. 1 can be used to input signals over a display surface of a display device (e.g., an LCD device). Referring to FIG. 1, the related art touch panel includes a viewing area V/A, corresponding to the display surface of the display device, and a dead space region 20, corresponding to a non-display region surrounding the viewing area V/A.
Referring to FIGS. 1 and 2, the related art touch panel includes rectangular upper and lower substrates 1 and 2 formed of a transparent material such as Polyethylene Terephtalate (PET) and bonded to each other via an insulating adhesive arranged in the dead space region 20. The insulating adhesive arranged in dead space region 20 ensures that the upper and lower substrates 1 and 2 are uniformly spaced apart from each other. First and second transparent electrodes 3 and 4, respectively, are formed over the entirety of the opposing surfaces of the upper and lower substrates 1 and 2, respectively. Next, metal electrodes (e.g., Ag paste) are formed in the dead space region 20.
More specifically, and while referring to FIG. 5A, first and second metal electrodes 5a and 5b, respectively, are formed in the dead space region 20 at left and right sides of the upper substrate 1 and are electrically connected to the first transparent electrode 3. A third metal electrode 5c is formed in the dead space region 20 at the upper or lower side of the upper substrate 1 and is electrically insulated from the first transparent electrode 3 by a first insulating layer 10a formed on the first transparent electrode 3. The third metal electrode 5c is, however, electrically connected to the second metal electrode 5b. The first and third metal electrodes 5a and 5c are electrically connected to an upper set of first and second signal lines, respectively, formed on a flexible printed circuit (FPC) 7 via a first conductive adhesive 8a while the second metal electrode 5b is connected to the upper second signal line within the FPC 7 via the third metal electrode 5c. 
Referring to FIG. 5B, fourth and fifth metal electrodes 6a and 6b, respectively, are formed in the dead space region 20 at lower and upper sides of the lower substrate 2 and are electrically connected to the second transparent electrode 4. A sixth metal electrode 6c is formed in the dead space region at the left side of the lower substrate 2, is electrically insulated from the second transparent electrode 4 by a second insulating layer 10b formed on the second transparent electrode 4, and electrically connects the fourth and fifth metal electrodes 6a and 6b to a lower set of first and second signal lines, respectively, formed on a lower surface of the FPC 7. The sixth metal electrode 6c is electrically connected to the lower set of first and second signal lines via a second conductive adhesive 8b while the fourth and fifth metal electrodes 6a and 6b are connected to the lower set of first and second signal lines, respectively, via the sixth metal electrode 6c. 
The upper and lower sets of first and second signal lines, arranged at upper and lower surfaces of the FPC 7, respectively, are connected to power source voltage source Vcc and a ground voltage source GND, respectively. Accordingly, the first and second transparent electrodes 3 and 4 are connected to Vcc and GND voltage sources via metal electrodes 5a–c and 6a–c, respectively.
As described above, the FPC 7 is electrically bonded to the first, third, and sixth metal electrodes 5a, 5c, and 6c, respectively, via the first and second conductive adhesives 8a and 8b, respectively, while the upper and lower substrates 1 and 2 are bonded to each other via an insulating adhesive 9, provided throughout the dead space region 20 except for a portion of the dead region occupied by the FPC 7.
To electrically connect the FPC 7 to the aforementioned metal electrodes, first and second conductive adhesives 8a and 8b are initially deposited on corresponding ones of the first, third, and sixth metal electrodes 5a, 5c, and 6c. Next, the insulating adhesive 9 is deposited within the dead space region 20, except for the portion of the dead space region occupied by the FPC 7. Subsequently, the portion of the FPC 7 that is to be electrically connected to the first, third, and sixth metal electrodes 5a, 5c, and 6c (e.g., the portions of the FPC 7 on which the first and second conductive adhesives 8a and 8b are formed) is heated to approximately 100° C. and pressed against the aforementioned metal electrodes. Accordingly, the FPC 7 can be electrically connected to the aforementioned metal electrodes. Upon electrically connecting the aforementioned metal electrodes to the FPC 7, the lower and upper substrates 1 and 2 become bonded to each other.
If, during operation of the related art touch panel described above, a predetermined portion of the upper substrate 1 is contacted with a contact object (e.g., a pen, a user's finger, etc.), the first and second transparent electrodes 3 and 4 electrically contact each other at a position corresponding to the location where the contact object contacted the upper substrate 1 (i.e., the contact point).
Accordingly, the power supply voltage Vcc and the ground voltage GND are applied to the right and left sides, respectively, of the first transparent electrode 3 via first, second, and third metal electrodes 5a–c connected to the upper set of the first and second signal lines formed on the upper surface of the FPC 7. Subsequently, a voltage, having a value made variable by a resistance or capacitance value specific to the contact point, is outputted via the second transparent electrode 4, the fourth, fifth, and sixth metal electrodes 6a–c, and the lower set of first and second signal lines formed on the lower surface of the FPC 7 such that an X-axis coordinate of the contact point is detected.
Next, the power supply voltage Vcc and the ground voltage GND are applied to the upper and lower sides, respectively, of the second transparent electrode 4 formed via the fourth, fifth, and sixth metal electrodes 6a–c connected to the lower set of the first and second signal liens formed on the lower surface of the FPC 7. Subsequently, a voltage value specific to the contact point is outputted to the first transparent electrode 3 and to the first, second, and third metal electrodes 5a–c of the upper substrate 1. Accordingly, a Y-axis coordinate of the contact point is detected.
Use of the aforementioned related art touch panel is disadvantageous, however, because it is difficult to uniformly maintain the distance to which the upper and lower substrates 1 and 2 are spaced apart from each other. Accordingly, the reliability with which the contact point is detected can be reduced due to the non-uniformly spaced-apart upper and lower substrates.